FIG. 14 is a block diagram of a conventional odor identifier 31. In FIG. 14, gas in the atmosphere is taken in through intake port 36, allowed to flow through sensor 34 installed in the path of piping 38, sent to exhaust pole 37 by pump 33 to be returned to the original atmosphere. At this time, an electric signal corresponding to the kind of the odor borne by the gas taken in is derived from sensor 34 and identification and concentration measurement of the odor are performed in data processor 35.
FIG. 15 is a schematic outside view of conventional odor identifier 31 configured as described above. Within main body 32, there are incorporated sensor 34, data processor 35, pump 33, and the like shown in FIG. 14. An ambient gas taken in as zero gas (reference gas) 42 and test gas (gas for test) 43 contained in test gas container 44 are alternately introduced into sensor 34 through intake port 36 at the top end of a sample probe projected from main body 32 and, thus, the kind of the odor, concentration, and the like of the test gas are measured.
However, with repetition of the measurement, the odorous component attaches sensor 34 and hence the zero level of sensor 34 gradually changes from its initial state and an accurate measurement becomes unattainable. Therefore, the zero gas is alternately taken in every time so that the zero level of sensor 34 is adjusted. The odor identifier is put into operation by manipulation of measurement start button 41 and the measured value is displayed on meter 40.
In conventional odor identifier 31, odor analysis is performed by detection of physical change or chemical change produced by adsorption of molecules of the odor component by the sensor material.
In a quartz crystal microbalance (QCM), for example, different kinds of adsorbents are applied to the surface of the quartz crystal and changes in mass produced by adsorption of the odor molecule by the adsorbents are detected by changes in number of vibration of the quartz oscillator. Since the kinds of chemical substances that are easily adsorbed differ with characteristics of the odor molecules, such as strength of polarity, the kind and quantity of the odor molecules constituting the odors can be estimated by measuring how much of change in the mass is produced in which of the adsorbents.
Adsorption of odor molecules can be detected not only by change in mass, but also by change in electric resistance, change in absorption wavelength of light, and the like, and there are proposed various sensors of such types. For example, such a sensor is put into practice that makes use of change in electric resistance when an odor molecule is adsorbed by a conductive polymer or by a composite material of an insulating polymer with conductive particles dispersed therein.
However, when sensor materials adsorbing odor molecules are used, it is unavoidable that the odor molecules remain on the surface of the sensor material or that a highly active molecule contained in the gas combines with the sensor material to thereby cause the quality of the sensor material to be changed.
Since, in such sensors, the sensor characteristic is changed by the history of its use, a relative difference, not an absolute value, of the sensor signal (the number of vibration for a quartz oscillator system, the electric resistance for a chemo resistor type, the absorption wavelength of light for an optical system, and so on) is mainly utilized. Since such a relative difference is measured as the difference in strength between signals from a reference gas (zero gas) not including the odor and from a gas for test (test gas), it is required to measure both the signals of the zero gas and the test gas in order to identify the odor.
Therefore, in the case of odor identifier 31 shown in FIG. 15, the odor is identified following such steps as, first, to measure the outside air, such as the room air, as the zero gas, and then, by inserting intake port 36 into container 44 such as a flask containing a sample, to measure the odor of the sample.
In this way, when identifying an odor with use of an odor identifier, it is required to measure both the test gas and the zero gas. In the case where the odor of a substance contained in a container is to be identified with use of odor identifier 31 shown in FIG. 15, the gas obtained by inserting intake port 36 into the container is used as the test gas and the gas obtained when intake port 36 is placed outside the container is used as the zero gas, and thus relative difference between the sensor signals is measured and the odor inside the container can be identified.
However, when an odor widely floating in the atmosphere surrounding the odor identifier is to be identified, it is impossible to take in the zero gas from the surroundings, and hence there has been a problem that the odor widely floating in the environment cannot be identified.
As an apparatus of the described type, there is disclosed an odor identifier with use of a zero gas container in Japanese Laid-open Patent Publication No. Hei 9-250979. However, this is not what aims at identification of an atmospheric odor. It is configured to take in the test gas, as well as the zero gas, from a container connected to the apparatus and it is not designed to be portable for identifying an atmospheric odor. Further, since the layout of the piping for making switchover between the zero gas and test gas is complicated and the switchover is troublesome, it is considered difficult to arrange this apparatus in a size suited for carrying.
Further, in Japanese Laid-open Patent Publication No. Hei 9-304244 is disclosed an odor identifier making it possible to identify an atmospheric odor by purifying the outside air and using the same as the zero gas. In this case, although consideration has been given to portability and identification of the atmospheric odor, the mechanism is complicated and switching is troublesome because measurement and purification of the outside gas is performed through valve change-over. Therefore, it is considered difficult to configure the apparatus in such a size that is capable of being incorporated into a small-sized household robot.
Further, in Japanese Laid-open Patent Publication No. 2000-155107, there is disclosed an odor identifier using a zero gas container in combination therewith. In this apparatus, identification or quantification of a sample gas is performed on the basis of a detected signal from the sample gas and a detected signal from the zero gas. However, the zero gas container is not of a built-in type and gas intake and exhaust is performed by use of a pump. Hence, variations are produced in the intake and exhaust quantities. Further, it produces noise and not made to be portable with the objective of being carried to measure an atmospheric odor. Further, since it is complicated in structure and requires valve change-over, it is considered that its operability is not good and configuring it in a portable size is difficult.
Further, in the conventional odor identifiers, there are such that use a fan or a diaphragm pump for gas intake. These are large in outer size and high in noise level when operated. Hence, these are not necessarily considered suited for portable use or incorporated use in a small-sized robot to be used in houses where quietness is desired.
Accordingly, an object of the present invention is to provide a gas detector capable of accurately measuring particular components (odors and the like) contained in an ambient gas which is desired to be measured and, further, being compact and capable of being easily arranged into a portable one, or producing low noise and capable of being small-sized.